1. Field of the Invention
The present invention relates to a recording apparatus and a recording method that records an image using a recording head provided with a plurality of recording elements.
2. Description of the Related Art
A recording head in an inkjet recording apparatus is provided with a plurality of nozzles (discharge ports) for discharging an ink, and discharge pressure generating elements (recording elements) are provided within respective nozzles. A high-quality of images, and a high-speed of recording are realized by arranging the plurality of nozzles in a high density.
Normally, ink droplets cannot be discharged at the same time from all of a plurality of nozzles of an inkjet recording head, and recording is performed at timings of the ink droplets discharge that are shifted for every group of a predetermined number of nozzles. As a method for shifting the discharge timings for every group of the predetermined number of nozzles, every group of the predetermined number of the nozzles is divided into sections based on physical positions of the nozzle arrays of the inkjet recording head, and drive timings of the discharge pressure generating elements of the nozzles within the divided sections are shifted from one another. In order that all nozzles within the section are driven within a predetermined period of time in a state where drive timings are shifted, each section is divided into a plurality of blocks, and the discharge pressure generating elements are driven in a time-division fashion for each block. When the discharge pressure generating elements are time-division driven for each block, the same block is simultaneously driven. As a result, inks are simultaneously discharged from one nozzle of each section. Such a time-division driving scheme is effective to make compact a power source for driving the inkjet recording head and power source members such as connectors or cables.
Now then, a number of nozzles that constitute the nozzle array of the recording head tends to increase year after year, and a recording head having a plurality of nozzle arrays in which a plurality of nozzles are arranged has come into use. Japanese Patent Application Laid-Open No. 2007-276353 discusses a method for recording image data (dot data) for one column by allocating it to a plurality of nozzle arrays. According to the recording method, in a case of recording the data, for example, by allocating it to two rows of the nozzle arrays, even if a driving frequency of each of the nozzle arrays is the same as that in a case of recording by only one row of the nozzle array, a recording speed can be doubled by doubling a scanning speed of the nozzle arrays. Further, if two rows of the nozzle arrays are used, one nozzle array is used only half a number of times to record a certain amount of region, for example, a region for one-scan, and as a result, lifetime of the recording head becomes longer.
Processing for distributing the dot data to a plurality of nozzle arrays such as two rows, or three rows or more is performed by, for example, a configuration illustrated in FIG. 1. FIG. 1 illustrates a configuration in which the image data (dot data) is divided for use in what is called multi-pass recording, and the recording head is driven based on the divided dot data, thereby carrying out recording. In FIG. 1, the image (dots) data input in step S201 is subjected to mask processing in step S202, and the dot data for a plurality of times of scans is generated. Then, in step S203, the divided dot data for the plurality of scans is assigned to the nozzles of respective nozzle arrays. Assignment of the dot data to the nozzle arrays is performed according to predefined pattern. In the present specification, the pattern is referred to as “drive pattern”.
FIG. 2 is a schematic diagram illustrating drive patterns for assigning discharge data to two rows of nozzle arrays. An example illustrated in FIG. 2 represents two nozzle arrays 1A and 1B that discharge same-colored inks, each having 16 pieces of nozzles arranged with an interval of 1200 dpi in a nozzle arrangement direction (in a vertical direction in FIG. 2). Nozzle numbers 1 to 16 beginning at the top nozzle are assigned to each of the nozzle arrays 1A and 1B. Further, an image to be recorded is what is called “solid image” (image in which ink dots are recorded in all areas (unit region where ink dots are recorded)) with a resolution of 1200 dpi. Then, a driving frequency of each nozzle of the nozzle arrays 1A and 1B corresponds to discharging with an area interval equivalent to 600 dpi at one time. In a case of a multi-pass recording, images assigned to two nozzle arrays correspond to images divided corresponding to a plurality of times of scans. In the above-described solid image, ink dots are recorded in areas of division ratio according to a number of times of scans, in each scanning. However, in the descriptions hereinbelow with reference to FIG. 2, in order to make descriptions easy to understand, a case will be described where the solid image is recorded by one scanning operation as an example.
In FIG. 2, with regard to the nozzle array 1A, the dot data is assigned according to the drive pattern “A”, and with regard to the nozzle array 1B, the dot data is assigned according to the drive pattern “B”. Block enable signals for performing time-division driving operation are input into the nozzle arrays 1A and 1B in the order from a nozzle with nozzle number 1 to a nozzle with nozzle number 16, and logical (AND) products with the dot data assigned according to the drive patterns are performed, and each of the recording elements is driven. More specifically, when a column (area array in the vertical direction in FIG. 2) 0 is recorded, in the nozzle array 1A, the recording elements corresponding to the nozzles with nozzle numbers {1,2}, {5,6,7}, {9,10}, {14} are driven in this order. On the other hand, in the nozzle array 1B, the recording elements corresponding to the nozzles with the nozzle numbers {3,4}, {8}, {11,12,13}, {15,16} are driven in this order. When the column 1 is recorded, both the nozzle arrays 1A and 1B record by the time-division driving using complementary nozzles excluding the nozzles used in the column 0. For the column 2 or later, the dot data of the column 0, and the dot data of the column 1 are alternately assigned.
In this way, even when respective nozzles are driven at a driving frequency to perform discharge with 600 dpi interval at one time, a drive equivalent to a driving frequency for discharging with 1200 dpi interval at one time can be performed. As a result, it becomes possible to record high-resolution images without slowing down recording speeds.
In the time-division driving scheme, an order of the recording elements to be driven exerts influence upon discharge performance of a head. More specifically, when liquid droplets are discharged from a certain nozzle, pressure wave of an ink is produced in a part which communicates with the nozzle, thereby causing an ink oscillation depending on a discharge frequency. The closer the part is to a generating source of oscillation, the larger the influence exerted by the oscillatory wave becomes, and adjoining nozzles are most susceptible to the oscillatory wave. Due to the influence, discharge state or discharge amount of the discharged ink becomes unstable. As a result, this may bring about poor image quality such as density (concentration) unevenness on the recorded images. For example, if the liquid droplets are discharged when a liquid level of the nozzle comes down, an ink mist becomes liable to be produced, which leads to deterioration of image quality of the recorded images. Further, energy with which the ink is discharged becomes larger, and thus lifetime of the head will be shortened. For this reason, a driving order of blocks is set such that occurrence of a phenomenon as described above is hindered.
Now, if the nozzle arrays are arranged in a plurality of rows, and the recording speed is multiplied, a beading problem may arise in the recorded images. More specifically, since the speed-up of the recording involves an increased amount of ink to be applied per unit time and per unit area of the recording medium, an ink absorption rate of the recording medium cannot respond to the application rate. Thus ink droplets which are not absorbed on the surface of the recording medium may come into contact with one another. Then, inks which have been combined by the contact and become relatively large are conspicuous in a finally obtained image, which may deteriorate image quality.
Conventionally, various recording methods and mask patterns for preventing the beading have been discussed. In Japanese Patent Application Laid-Open No. 2009-39944, for example, there is described a use of mask designed to attain a high dispersability of dot arrangement which the nozzle array records by one-time scan in a multi-pass recording. According to this patent, by the high dispersability of the recorded dots between the divided patterns, chances that inks come into contact with one another by the one-time scan can be reduced. That is, a beading problem which deteriorates image quality can be alleviated.
However, the image data is not divided only by the mask patterns, but the image data is also divided by the drive patterns. In this case, if a size in a conveyance direction of the drive pattern stays constant, the following problem arises. More specifically, if the recording data is allocated based on the drive pattern, images are formed at a repetitive cycle depending on the size of the drive pattern. However, when a conveyance amount of multi-pass recording at one time is not an integral multiple of the size in the conveyance direction of the drive pattern, the drive patterns of the recording head will vary from scan to scan in the unit region. At this time, interference will occur between the mask patterns and the drive patterns, and dot dispersability of images will be degraded, thereby the dots become prone to coming into contact with one another, and the above-described beading may occur.